1. Field of the Invention
The present invention relates to a process of and an apparatus for sealing a thermoplastic resin sheet and is applicable, e.g., to a blister package used for packing foods, daily needs, medicines and the like.
2. Description of the Related Art
The blister package (PTP package), made by a process of providing pockets on a thermoplastic resin sheet so as to correspond with the shape of a packaged article, placing the article therein and subsequently sealing the pockets with a mount such as an aluminum foil, was conceived in Europe and has been used in Japan since the first half decade of the 1960's.
A sealing plate or a sealing roller has been employed through a conventional sealing process for the blister package. When using the sealing plate 61 so as to be shown in FIG. 16, a thermoplastic resin sheet 62 already formed with pockets (not shown) is fed into a seal-receiving plate 63, where a mount 65 such as aluminum foil supplied from a supply roller 64 is sealed to the sheet 62 by a seal plate 61. As shown in FIG. 17, the seal plate 61 has thereon a convex portion 66 in the crosshatched pattern to thereby form a sealing having the crosshatched pattern at a sealing portion between the sheet 62 and the mount 65.
Another conventional sealing process using the seal roller is shown in FIG. 18. A thermoplastic resin sheet 51 already formed with pockets is fed into a seal-receiving roller 52, where a mount 54 supplied from a supply roller 53 is sealed to the sheet 51 by a seal roller 55. As shown in FIG. 19, the sealing roller 55 has thereon a convex portion 56 in the crosshatched pattern to thereby form a sealing having the crosshatched pattern at a sealing portion between the sheet 51 and the mount 54.
However, a large pressure for sealing and a precise surface are inevitable when using the seal plate 61, so that the seal roller has gradually come to be large.
According to the conventional sealing process using the roller 55 as described above, when intending to enlarge an area to be sealed and speed up the process for sealing a material for packaging such as polypropylene (PP) with a mount, some problems come to appear. Some of those are the appearance of the nonuniformity of bite between the mount 54 and the sheet 51 and the deterioration and nonuniformity of sealing strength.
In order to overcome the above problems, some changes were tried, including:
(1) the sealing temperature is raised;
(2) the sealing pressure is increased;
(3) the crosshatched pattern of the convex portion 56 is modified; and
(4) the seal base film (Aluminum foil sealant) is modified to attain fine sealing.
However, there resulted a fuming, a burning and a deformation of an article to be packaged because of trying (1). By trying (2) and (3), some cracks of the aluminum foil appeared by pinholes. When trying (4), the visible bite appearance is not in fine condition, while the sealing temperature of polypropylene can be approximately decreased to 180.degree. C.
An object of the present invention is to provide a process of and an apparatus for sealing a thermoplastic resin sheet under a low temperature and a high speed in operation.